<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/JavaScript">
function fn1() {
var _div = document.getElementById("div1");
fnShowDiv(_div);
}
//显示指定DIV
function fnShowDiv(_div) {
var iWidth = document.documentElement.clientWidth;
var iHeight = document.documentElement.clientHeight + document.documentElement.scrollTop * 2;
var h = 70; //div 高
var w = 260; //div 宽
_div.style.top = (iHeight - h) / 2 + "px";
_div.style.left = (iWidth - w) / 2 + "px";
_div.style.display = "block";
_div.style.position = "absolute";
_div.style.width = w + "px";
_div.style.height = h + "px";
_div.style.textAlign = "center";
_div.style.margin = "0 auto";
_div.style.background = "red";
}
</script>
</head>
<body>
<div id="div1" style=""></div>
<input type="button" id="btn1" style=" margin:700px auto" value="测试" onclick="fn1()" />
</body>
</html>
原文：http://www.cnblogs.com/liwentao/p/7124207.html